Astronomers recently found another ring around the planet Saturn   -- and it's the biggest one yet. This newly discovered ring stretches about 15 million miles across, which makes a loop big enough to fit a billion Earths inside. It may be even bigger and reach 22 million miles across at its diameter  . Saturn's new ring is now the biggest known ring in the solar system.  This ring, like Saturn's other rings, is not one solid piece of rock. Instead, it is made up of millions or billions of tiny rocks that orbit   the planet all together and give the appearance of a unified   ring. Unlike the more visible rings, however, this big one is mysterious -- the pieces are far apart, and the ring cannot be seen from the surface of the Earth. If all the pieces were stuck together, they'd be slightly bigger than a rock a half-mile wide. Astronomers suspect that the newly discovered ring gets its material from Saturn's outermost   moon, Phoebe. For example, the dust in the ring circles Saturn in the same path and the same direction as Phoebe. Plus, the surface of Phoebe is marked with holes and places where rock has been knocked away, the result of collisions between Phoebe and other moons and rocks. These collisions could have sent dust out into space to become part of the big ring. The discovery of the ring could help explain other mysteries surrounding Saturn and its dozens of moons. The moon called Iapetus, for example, is two-toned: one side is gray; the other more reddish. Iapetus is within the newly discovered ring, but it orbits in the opposite direction. As a result, some researchers say, debris   from the ring may have coated and color1ed one side of Iapetus as it moved through space, and left the other side alone. "The cause of Iapetus' strange color1 distribution ... has been a puzzle that now seems solved," said Joseph Burns, a scientist. But not everyone agrees. Some think the ring alone may not be able to explain Iapetus' funny color1ing. The main reason why one side of Iapetus is gray may be that   _  . A) Saturn's moons move in the same direction B) there are many moons circling around Saturn C) debris from the biggest ring covers one side of Iapetus D) Iapetus strikes against other moons while moving
C

Some 30,000 years ago, artists who lived in caves in Europe painted pictures of the animals around them: panthers, hyenas, rhinos, cave lions, mammoths and other creatures which have been extinct for a long time. The paintings were highly realistic. Some even showed movement. The artwork, more than a thousand drawings, is considered the oldest group of human cave drawings which have ever been discovered. They were preserved because the cave was sealed---closed off--for more or less 23,000 years. Fast forward to December 18, 1994, a group of French cave scientists were exploring caves in southern France. Jean Marie Chauvet, who led the group then, describes the process of discovering the cave paintings. "At that time I was in the front, Eliette just walked behind me, Christian behind. Eliette said she saw two marks with red ochre and she said, 'They came here.' And at this very moment everything began. The drawings and everything linked to the parietal art . That is where it is tarted." Cave art expert Jean Clotttes reviewed the paintings. "I was amazed at the number of paintings there were and paintings of their quality and particularly in front of the panel of the horses." Scientific analysis confirmed the prehistoric date of the artwork. Studies showed the drawings were created tens of thousands of years ago, before human history was written. The United Nations' cultural agency UNESCO lists the cave as a World Heritage Site. They say that the drawings form a remarkable expression of early human artistic creation of grand excellence and variety. The Chauvet Cave has been named after the explorer who first entered it. However, its environment and drawings are too fragile to be visited by human beings. So the cave is closed, and only people there for scientific purposes can go inside and see the artwork. However, French authorities asked experts to create an exact copy of the cave, called Pont d'Arc Cavern. The copy, which we also called replica, cost more than 59 million dollars to build. It opened at the end... Which of the follow statements is TRUE about the Chauvet Cave? A) It was closed off for more than 30,000 years. B) It is thought to be the origin of modern parietal art. C) The environment and artwork there are very easy to damage. D) The majority of drawings there are about the extinct animals.
C

Hong Kong, a city of seven million--and growing fast. By the year 2050 Hong Kong's population will almost double. Where will these people live? There's only one place to go--up. Fast forward 50 years.This is the tallest man-made structure on the planet. Its name:Millennium Tower. It would stand twice as tall as anything built before. Over 60 thousand people would live or work here. Millennium's designers think it represents the best solution for the coming population explosion. It would cost ten billion dollars and consume more building materials than any single nation could produce. David Nelson, one of Millennium's key designers, said:"It would be a massive project and a world project. But to actually realize it, resources would have to come from all over the globe. The challenge and the motivation for doing it would be to realize one of the world's largest and most complex construction projects." Millennium would be more complex than anything ever built. So its builders won't know for sure the building is safe until it's up, and they can't afford to make an error. Massive earthquakes have brought down entire cities in this part of the world. Can Millennium's designers make it immune to these quakes of the earth? For Millennium, like all the other buildings, safety is just one concern among many. It will need to be a home, one that welcomes people in. Getting people into the building and making sure they have a great experience well be what makes Millennium successful, but how to do it? For the design team, the secret was to bring all the elements of city life within. Cafes and restaurants, theatres and stores would provide entertainment. Health clubs, even schools and medical clinics would also serve the towers' residents. Millennium's designers have proven something. Things that seem impossible today, might just become reality tomorrow. The engineering problems have, for the most part, already been solved. Our achievements are limited only by our imaginations. Why did the designers decide to build Millennium? A) Because they wanted to build the world's most complex building. B) Because Hong Kong's population will greatly increase. C) Because Hong Kong is developing fast as an international city. D) Because it can bring huge profit after it is put to use.

B